As previously described in U.S. Pat. No. 5,851,446 to Bardo, et al (1998) and U.S. Pat. No. 5,902,522 to Seawell, et al. (1999), of which some portions are reproduced hereinafter, cooling towers are used to cool liquid by contact with air. Many cooling towers are of the counter-flow type, in which the warm liquid is allowed to flow downwardly through the tower and a counter current flow of air is drawn by various means upward through the falling liquid to cool the liquid. Other designs utilize a cross-flow of air, and forced air systems. A common application for liquid cooling towers is for cooling water to dissipate waste heat in electrical generating and process plants and industrial and institutional air-conditioning systems.
Most cooling towers include a tower or frame structure. This structural assembly is provided to support dead and live loads, including air moving equipment such as a fan, motor, gearbox, drive shaft or coupling, liquid distribution equipment, such as distribution headers and spray nozzles, and heat transfer surface media such as a fill assembly. The fill assembly material generally has spaces through which the liquid flows downwardly and the air flows upwardly to provide heat and mass transfer between the liquid and the air. Different types of fill materials, e.g., stacked layers of open-celled clay tiles, are commercially available, depending on the desired design and operating characteristics. This fill material is heavy, and can weigh in excess of 50,000 pounds for a conventional size air conditioning cooling tower. As such, the tower frame/structure and other structural parts of a cooling tower must not only support the weight of the fill material and other components, but must also resist wind forces or loads and should be designed to withstand earthquake loads.
Due to the corrosive nature of the great volumes of air and water drawn through such cooling towers, it has been the past practice to either assemble such cooling towers of stainless steel or galvanized and coated metal, or for larger field assembled towers, to construct such cooling towers of wood, which is chemically treated under pressure, or concrete at least for the structural parts of the tower, or combination of these materials.
Metal structures and parts of cooling towers can be corroded by the local atmosphere or the liquid that is being cooled, depending on the actual metal used and the coating material used to protect the metal. Further, such metal towers are usually limited in size and are also somewhat expensive, especially in very large applications such as for cooling water from an electric power generating station condenser. Concrete is very durable, but towers made of concrete are expensive and heavy. Many cooling towers are located on roofs of buildings, and the weight of a concrete cooling tower can present building design problems. Plastic parts are resistant to corrosion, but prior plastic parts ordinarily would not provide enough strength to support the fill material and the weight of the tower itself.
Wood has been used for the structural parts of cooling towers, but wood also has its disadvantages. Wood towers may require expensive fire protection systems. The wood may decay under the constant exposure not only to the environment, but also to the hot water being cooled in the tower. Wood that has been chemically treated to increase the useful life may have environmental disadvantages: the chemical treatment may leach from the wood into the water being cooled. Fiber reinforced plastic has been used as a successful design alternative to wood and metal.
Within the last decade or so, prior art solutions began using fiber reinforced plastic beams and columns including those shown in U.S. Pat. No. 5,236,625 to Bardo (1993) and U.S. Pat. No. 5,028,357 to Bardo (1991), both of which are incorporated herein by reference. Both patents disclose prior art structures for cooling towers. Thus, while these prior fiber-reinforced plastic tower structures have solved many of the problems associated with wood and metal cooling tower structures, the solutions to the problem of resistance to lateral loading have increased the costs of these units. Both the shear wall and laterally braced frames can be labor intensive to build, since there are many parts and many connections to be made. With these prior art solutions, there exist a large number of key structural elements, with more complex manufacturing and inventorying of parts, increasing the complexity of construction, and therefore the costs.
As such, a need existed for a lower cost cooling tower structure, and for lower cost cooling tower structures that meet less exacting design criteria. Further, in those fiber reinforced plastic frame structures at the time, one difficulty with the joint between the columns and beams was that when constructed with conventional bolts or screws, the beams and columns could rotate with respect to each other. When tighter connections were attempted to be made with conventional bolts or screws to limit the rotation and provide lateral stability without adding diagonal bracing, the fiber reinforced plastic material could be damaged, and the problem worsened as the connecting members might degrade the fiber reinforced plastic and enlarge the holes in which they are received.
Some of the problems of these prior art systems were alleviated or reduced with new fiber reinforced cooling tower systems and methods of construction as described in U.S. Pat. No. 5,851,446 to Bardo (1998) and U.S. Pat. No. 5,902,522 to Seawell (1999), both of which are incorporated herein by reference. As described therein, the fiber-reinforced plastic (FRP) beams and columns were connected using mounting plates and bonding adhesive. As noted in these patents, one advantage of this prior art system allows a theoretical increase in the size of the bays, instead of the standard bay with columns spaced apart a distance of six feet, such bays arguably can be increased to provide bays with up to twelve feet between columns. However, the use of mounting plates and bonding adhesive increases the number of components, time and expense in assembling the structure. Moreover, larger bays constructed in accordance with prior art structures may be unlikely to meet the design criteria necessary to support the cooling tower components and structures, unless larger, stronger and more costly components are utilized.
Accordingly, a cooling tower and tower/frame structure having fewer beams and columns, and fewer overall components, that reduced costs and time to assemble, has been developed, such as that described in U.S. Pat. No. 7,275,734, which is incorporated herein by reference.
Another problem with prior art cooling towers is the type of cooling employed to cool the liquid is limited to either “wet cooling” or “dry cooling”. In wet cooling, the liquid is cooled by direct contact with the air flow. In dry cooling, the liquid is cooled by the air flowing across a thermally conductive heat exchanger (e.g., coils) that carries the liquid. Normally, cooling towers employ either wet cooling or drying cooling, but not both. Under certain operating and environmental conditions, wet cooling towers can emit a visible plume (caused by evaporation of the liquid). These visible plumes are undesirable for several reasons. Thus, cooling towers have been recently designed to provide “plume abatement”—which is the reduction or elimination of the visible plume. To accomplish this, manufacturers of wet cooling towers have incorporated technology which dries the air and reduces/eliminates the plume. A wet cooling tower with plume abatement technology has been referred to as a “hybrid cooling tower.” In these towers, features and components normally used in drying cooling are utilized for the limited purpose of plume abatement (i.e., drying the saturated air to reduce/eliminate the visible plume).
Accordingly, there is needed a new cooling tower design that utilizes both dry and wet cooling structures and techniques in which the cooling mode may be dry cooling only, wet cooling only, or a combination of dry and wet cooling. In addition, the combination of dry and wet cooling allows for plume abatement when necessary or desirable.
Still another problem with prior art cooling towers is the fill material. Different types of fill materials, e.g., stacked layers of open-celled clay tiles, are commercially available, depending on the desired design and operating characteristics. The specific shape and composition of different fill materials may result in less or more cooling capacity and efficiencies. Accordingly, there is needed a fill material having different shape(s) and/or composition(s) to improve cooling tower performance.